1.

The initial rate of hydrolysis of methyl acetate (1" M") by a weak acid (HA, 1 M) is 1//100th of that of a strong acid (HX, 1 M) at 25^(@)C. The K_(a) of HA is

Answer»

`1xx10^(-4)`
`1xx10^(-5)`
`1xx10^(-6)`
`1xx10^(-3)`

SOLUTION :Rate w.r.t. weak acid, `R_1=k [H^+]_(WA)` [ ESTER]
Rate w.r.t. strong acid, `R_2=k[H^+]_(SA)` [ ester ]
`:.""R_1/R_2=([H^+]_(WA))/([H^+]_(SA))=1/100"(Given)"`
`:.""[H^+]_(WA)=([H^+]_(SA))/(100)=1/100xx1M=0.01M`
`=10^(-2)M`
`HAhArrH^++A^-`
Initial`"C mol L"^-1`
At eqm. ` C-Calpha""Calpha""Calpha`
`=C(1-alpha)`
`[H^+]=Calpha" or "10?^-2=1xxalpha" or "alpha=10^-2`
`K_a=(Calpha.Calpha)/(C(1-alpha))=(Calpha^2)/(1-alpha)~~Calpha^2`
`=1xx(10^-2)=10"^-4`


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